Organic semiconductor materials have become important components of materials such as flexible, thin film transistors and lightweight photovoltaic cells. The transistors typically comprise a substrate, a dielectric, a source electrode, a drain electrode, and a gate electrode in addition to the semiconductor. A variety of processes can manufacture these devices such as inkjet printing and thermal evaporation. The performance of these devices improves with increases in the mobility of charge carriers in the semiconducting material. Polymeric materials such as poly(3-hexlythiophene) (P3HT) or poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) are sometimes employed as the organic semiconductor material. The term polymer is commonly employed to mean a molecule formed by linking together a sequence of identical molecular units called monomers. The length of a polymer consisting of N monomers will be N times the length of the monomer, and the molecular weight of the polymer will be N times the molecular weight of the monomer. Another type of polymer, a co-polymer, is formed by linking together a sequence of at least two types of monomers. The length, or molecular weight, of such a polymer will be the sum of the lengths, or molecular weights, of the monomers. An alternating co-polymer could be specified as A-D-A-D . . . A-D where A and D represent distinct monomers. Indacenodithiophene-co-benzothiadiazole is an example of a co-polymer. Polymeric materials are advantageous because they can be incorporated into a device inexpensively by solution processing, and can achieve mobility of 0.1 to 1 cm2/Vs.
One approach to increasing the mobility of the charge carriers, holes and electrons, in organic semiconductor materials enhances the electronic connectivity between ordered domains.